Do we actually have to live with his parents for the first year?

The cards are printed and November is close, which means the timeline you were handed yesterday was decided long before you were told. Moving into a shared ground floor when you have never lived away from your own home is a massive leap, and doing it with an indefinite end date tied to a brother's flat in 2026 makes it harder. Vague timelines tend to stretch, and 2026 is a long time to put your newlywed life on hold. Your parents are giving you the standard script because joint households are familiar to them, but familiarity does not mean it will feel easy for you. The cost of pushing back right now is immediate friction. You will upset the household before you even move in, and your fiancé will likely feel caught between his mother and his bride. He needs to be the one who talks to his parents about a hard stop for this arrangement. You and your fiancé need to sit down tonight and agree on what happens if that flat in 2026 gets delayed. You can tell him that you want to support his family, but you need a firm commitment that the two of you will have your own kitchen space or a locked-off portion of the house within a set number of months, regardless of what his brother does. If he cannot give you that guarantee now, the ground floor arrangement will become permanent by default. Practise saying something direct to him like, I cannot live in a shared space indefinitely, and we need a written plan for our own place before the wedding happens.